Italian pronunciation (southern dialect/Neapolitan) of the word "Madonna", literally referring to the Virgin Mary (the mother of Christ). Equivalent would be "Holy Smokes".. A phrase to represent surprise, amazement, or down right shock. Could be used in many contexts.

"oh Marone a mi, who let one go?"
"Marone, this guy complains more than Woody Allen..."
"Marone, you yap worse than 6 barbers."

In the Sopranos episode when Paulie visited Tony in the hospital while in a comma. Paulie in shock proclaims "uff Marone, he looks terrible!"